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The prevailing view about molecular catalysts is that the central metal ion is responsible for the reaction mechanism and selectivity, whereas the ligands mainly affect the reaction kinetics. Here, we question this paradigm and show that ligands have a dramatic influence on the selectivity of the product. We show how even a seemingly small change in ligand isomerization sharply alters the selectivity of the well‐researched oxygen reduction reaction (ORR) Co phthalocyanine catalyst from an indirect 2e− to a direct 4e− pathway. Detailed analysis reveals that intramolecular hydrogen‐bond interactions in the ligand activate the catalytic Co, directing the oxygen binding and thus deciding the final product. The resulting catalyst is the first example of a Co‐based molecular catalyst catalyzing a direct 4e− ORR via ligand isomerization, for which it shows an activity close to the benchmark Pt in an actual H2−O2 fuel cell. The effect of the ligand isomerism is demonstrated with different central metal ions, thus highlighting the generalizability of the findings and their potential to open new possibilities in the design of molecular catalysts. [ABSTRACT FROM AUTHOR]

Abstract: Bipolar junction transistors (BJTs) can function as electrically reversible switches; nevertheless, triggering such circuits requires a distinct voltage bias at the base terminal. Here, we show a proof‐of‐concept of an electrochemical switching device equipped with a redox electrode whose bi‐stable interfacial chemistry, reliant on hydronium ion strength, can provide distinct logic HIGH (1) and logic LOW (0) levels of operation, enabling it to control and command an electronic circuit without the aid of any external voltage input. Electrochemical impedance spectroscopy, quartz crystal microbalance studies, and UV/Vis spectroscopy demonstrate that discrete logic levels are controlled by the solvent‐mediated charge injection/ejection kinetics at the redox‐active half‐cell electrode, leading to a chemically reversible switch with a response time of approximately 1 s and an operating speed of 225 cycles per hour. We demonstrate that the logic HIGH level of the interfacial twin states is actuated when exposed to acid‐contaminated wastewater, automatically triggering the command for remediation. [ABSTRACT FROM AUTHOR]

In a fuel cell, almost 80% efficiency loss arises due to the cathode; consequently, the cathode requires the largest amount of precious metal catalyst. Here, we show a precious-metal-free cathode for a proton exchange membrane fuel cell (PEMFC) containing only carbon nanoparticles as the catalyst and a freely diffusing molecule as the electron acceptor. Factors controlling the true rate of electrochemical reactions are amplified just by using carbon nanoparticles, leading to a carbon corrosion-free PEMFC delivering 154 mW/cm2 at 358 mA/cm2 without any precious metals. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) is impermeable to H2 and O2 fuels while permitting H+ shuttling, making it a potential candidate for proton exchange membrane fuel cells (PEMFC), albeit with a large anisotropy in their proton transport having a dominant in plane (sIP) contribution over the through plane (sTP). If GO-based membranes are ever to succeed in PEMFC, it inevitably should have a dominant through-plane proton shuttling capability (sTP), as it is the direction in which proton gets transported in a real fuel-cell configuration. Here we show that anisotropy in proton conduction in GO-based fuel cell membranes can be brought down by selectively tuning the geometric arrangement of functional groups around the dopant molecules. The results show that cis isomer causes a selective amplification of through-plane proton transport, sTP, pointing to a very strong geometry angle in ionic conduction. Intercalation of cis isomer causes significant expansion of GO (001) planes involved in sTP transport due to their mutual H-bonding interaction and efficient bridging of individual GO planes, bringing down the activation energy required for sTP, suggesting the dominance of a Grotthuss-type mechanism. This isomer-governed amplification of through-plane proton shuttling resulted in the overall boosting of fuel-cell performance, and it underlines that geometrical factors should be given prime consideration while selecting dopant molecules for bringing down the anisotropy in proton conduction and enhancing the fuel-cell performance in GO-based PEMFC. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) is impermeable to H2 and O2 fuels while permitting H+ shuttling, making it a potential candidate for proton exchange membrane fuel cells (PEMFC), albeit with a large anisotropy in their proton transport having a dominant in plane (sIP) contribution over the through plane (sTP). If GO-based membranes are ever to succeed in PEMFC, it inevitably should have a dominant through-plane proton shuttling capability (sTP), as it is the direction in which proton gets transported in a real fuel-cell configuration. Here we show that anisotropy in proton conduction in GO-based fuel cell membranes can be brought down by selectively tuning the geometric arrangement of functional groups around the dopant molecules. The results show that cis isomer causes a selective amplification of through-plane proton transport, sTP, pointing to a very strong geometry angle in ionic conduction. Intercalation of cis isomer causes significant expansion of GO (001) planes involved in sTP transport due to their mutual H-bonding interaction and efficient bridging of individual GO planes, bringing down the activation energy required for sTP, suggesting the dominance of a Grotthuss-type mechanism. This isomer-governed amplification of through-plane proton shuttling resulted in the overall boosting of fuel-cell performance, and it underlines that geometrical factors should be given prime consideration while selecting dopant molecules for bringing down the anisotropy in proton conduction and enhancing the fuel-cell performance in GO-based PEMFC. [ABSTRACT FROM AUTHOR]

The prevailing view about molecular catalysts is that the central metal ion is responsible for the reaction mechanism and selectivity, whereas the ligands mainly affect the reaction kinetics. Here, we question this paradigm and show that ligands have a dramatic influence on the selectivity of the product. We show how even a seemingly small change in ligand isomerization sharply alters the selectivity of the well-researched oxygen reduction reaction (ORR) Co phthalocyanine catalyst from an indirect 2e - to a direct 4e - pathway. Detailed analysis reveals that intramolecular hydrogen-bond interactions in the ligand activate the catalytic Co, directing the oxygen binding and thus deciding the final product. The resulting catalyst is the first example of a Co-based molecular catalyst catalyzing a direct 4e - ORR via ligand isomerization, for which it shows an activity close to the benchmark Pt in an actual H 2 -O 2 fuel cell. The effect of the ligand isomerism is demonstrated with different central metal ions, thus highlighting the generalizability of the findings and their potential to open new possibilities in the design of molecular catalysts., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Contrary to conventional beliefs, we show how a functional ligand that does not exhibit any redox activity elevates the charge storage capability of an electric double layer via a proton charge assembly. Compared to an unsubstituted ligand, a non-redox active carboxy ligand demonstrated nearly a 4-fold increase in charge storage, impressive capacitive retention even at a rate of 900C, and approximately a 2-fold decrease in leakage currents with an enhancement in energy density up to approximately 70% via a non-electrochemical route of proton charge assembly. Generalizability of these findings is presented with various non-redox active functional units that can undergo proton charge assembly in the ligand. This demonstration of non-redox active functional units enriching supercapacitive charge storage via proton charge assembly contributes to the rational design of ligands for energy storage applications., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)